Current sensorless control of a boost-type switch mode rectifier (smr) with inductor parameter adaptation

ABSTRACT

Boost-type switch-mode rectifiers (SMR) commonly use a resistor or a magnetic current sensor to measure the instantaneous input or inductor current that is used as the feedback to the current controller. A novel current sensorless scheme is described that computes the inductor current from the measured inductor voltage in a single-phase boost-type SMR using an adaptive low pass filter. This calculation requires an estimate of the inductance and the equivalent series resistance of the inductor coil. Both these parameters are dependent on operating conditions and are updated continuously. This is done using an adaptive model of the inductor that computes these parameters of the inductor once in every half cycle of the input current. The adaptation scheme is robust against parameter variations. Simulation and experimental results confirm the effectiveness of the proposed technique which provides comparable performance to standard measured feedback current scheme both under steady-state and transient conditions.

FIELD

The disclosure pertains to the elimination of current sensing resistorsin a boost type SMR by estimating the inductor current from the inductorvoltage while keeping total harmonic distortion (THD) low and increasingthe efficiency of the SMR by eliminating the current sensing resistor.

BACKGROUND

The classical control scheme for a typical switch-mode rectifier asshown in FIG. 1 employs two cascaded feedback control loops; the innercurrent loop for input current shaping and total harmonic distortion(THD) minimization and the outer voltage loop for output voltageregulation. For minimizing THD average current control is preferred. Theinductor current which is used as the feedback signal for averagecurrent control is normally sensed using either a resistor in serieswith the inductor or a magnetic current sensing device such as HallEffect based current sensor or regular current transformer. Resistorsensing is usually very straightforward, particularly in low powercircuits, where the power dissipation in the sense resistor isnegligible. However, in many applications, using a current senseresistor in the direct path of the current to be measured is notpractical as not only a small value of sense resistor is difficult toimplement, but also the power loss in the sense resistor is too high,particularly in large power converters. Also this sense resistor needsconnection to the high voltage section of the circuit and henceisolation of the low voltage control circuit can become an issue. HallEffect current sensors are reliable but suffer from dc offset, highercost, temperature issues and the need to have a separate power supply. Asingle ferrite core current transformer (CT) cannot be directly used tosense the inductor current as it has a dc offset. To circumvent thisproblem two CTs can be used, one for sensing the switch current and onefor sensing the diode current. By summing these two currents the trueinductor current can be reconstructed [1]. Other options include coppertrace resistance sensing with temperature compensation electronics,Rogowski coils, magneto resistance sensors and fiber-optic currentsensors. Their applications are limited by isolation issues, high cost,size, incapability of measuring direct currents, low accuracy, orunsuitability for small currents [2,3].

From the above discussion it is clear that there is a need for anaccurate, sensorless current measurement or estimation scheme. The vastbody of literature related to research on sensorless current estimationtechniques also confirms this viewpoint. They are briefly reviewed inthe next few paragraphs.

In [4-6], the reference current is generated from input and outputvoltage without current sensing. The turn-off instant of the switch iscalculated based on the maximum value of the reference current in aswitching instant. The peak of the ramp carrier signal is proportionalto the output dc voltage. The control law makes the peak current in eachswitching period follow v_(d). The drive signal delay, sample and holddelays and measured voltage offset error can also be compensated.However compensation technique is utility voltage and load dependent andresearch is still required to make it tunable for any operating point.The scheme has been implemented using a field programmable gate array(FPGA).

Since under continuous conduction mode (CCM) the input-outputrelationship of a boost SMR is given by (1), it logically follows thatvarying a duty cycle, d, which is modulated because of the sinusoidalnature of the voltage waveform v_(d), would essentially result in asinusoidal input current; with the output voltage V_(o) maintainedconstant by a closed loop controller. Thus researchers followed thislead and came up with many improved versions of this basic scheme [7-11]that add a term which is proportional to the derivative of v_(d). Thisis because the derivative of the inductor current i_(L) should beideally proportional to the instantaneous values of v_(d) as shown by(2). Following FIG. 1, the voltage across the boost inductor L,neglecting the series resistance R_(L) can be written as (3). v_(Q), thevoltage across the switch Q can also be written in terms of the outputvoltage V_(o) as (4). Substituting i_(L) and v_(Q) from (2) and (4)respectively in (3) one can obtain an improved version of (1) as shownin (5).

$\begin{matrix}{{= {1 - \frac{\nu_{d}}{V_{o}}}}} & (1) \\{i_{L} = {\kappa_{1} \cdot \nu_{d}}} & (2) \\{{L\frac{i_{L}}{t}} = {\nu_{d} - \nu_{Q}}} & (3) \\{\nu_{Q} = {\left( {1 - } \right)V_{o}}} & (4) \\{{= {1 - \frac{\nu_{d}}{V_{o}} + {\frac{\kappa_{2}L}{V_{o}}\frac{\nu_{d}}{t}}}}} & (5)\end{matrix}$

A further improved version of (5) includes the inductor equivalentseries resistance, the voltage drop across the rectifier diodes, andalso the drops across the switch and the diode in the boost converter[12]. References [13] and [14] sense only the input voltage to implement(5). Discrete time domain versions of (5) suitable for microcontrollerimplementation with or without compensating for circuit non-idealitiesusing stored or computed duty cycle patterns have also been examined in[15-19].

A different approach is followed in [20-24] to achieve a currentsensorless boost-type SMR. The voltage loop output in the form of aphase angle α, is used to control the output voltage along with theshape of the input current, as given by (6). Compensation for circuitnon-idealities such as inductor resistance and device drops are alsopossible. While most of them are single loop, a two loop implementation,with one loop for phase angle and one for mean output voltage controlthrough real power control; using Kalman filters have been implemented[23].

$\begin{matrix}{{d = {1 - {\frac{{\hat{v}}_{d}}{v_{0}}{{\sin \left( {\theta - \alpha} \right)}}}}};{v_{d} = {{\hat{v}}_{d}{{\sin (\theta)}}}}} & (6)\end{matrix}$

TABLE I Prior-art in the area of current sensorless control of singlephase boost-type SMR. [7] [10] [13] [15] [21] [4-6] [8] [9] [11] [12][14] [16] [17] [18] [19] [20] [22] [23] [24] [25] Takes circuit No No NoNo Yes No No Yes No No No Yes No Yes No non- idealities in to accountProven to be Yes¹ No Yes² No No No No No No No No  Yes³ No  Yes⁴ Noinsensitive to parameter variation ¹Not verified with experimentalresults. ²Analyzed input admittance for inductance variations.³Experimental results have been obtained with non-nominal inductance andcapacitance. ⁴Detailed experimental results have been provided onparameter variation.In [25], the current is indirectly measured by connecting a capacitor inseries with a resistor across the boost inductor. If v_(C) _(s) (s) andi_(L)(s) are respectively the capacitor voltage and inductor current infrequency domain, it can be shown that

$\begin{matrix}{\frac{v_{C_{s}}(s)}{i_{L}(s)} = {\frac{R_{L} + {sL}}{1 + {{sR}_{C_{s}}C_{s}}} = {{R_{L}\frac{1 + {s\frac{L}{R_{L}}}}{1 + {{sR}_{C_{s}}C}}} = {R_{L}\frac{1 + {s\; \tau_{L}}}{1 + {s\; \tau_{C}}}}}}} & (7)\end{matrix}$

where R_(L), R_(C) _(s) are respectively the equivalent seriesresistance of the boost inductor L and the external resistor connectedin series with the current sense capacitor C_(s). If τ_(C)=R_(C) _(s)C_(s) is chosen so that it matches

${\tau_{L} = \frac{L}{R_{L}}},$

the relation

$\frac{v_{C_{s}}}{i_{L}}$

becomes frequency independent, signifying that the sensing preserves theshape of the inductor current. Under this condition, v_(C) _(s) isproportional to the inductor current and therefore can be used in thecurrent control loop. Obviously, the technique is load dependent as boththe inductor resistance and the inductor value are influenced by theinductor current. Reference [26] presents a similar technique applied toa dc-dc buck converter using a self-tuning digital filter whoseparameters are tuned using a test current sink, consisting of a knownresistor in series with a small switch, in parallel with the load. TableI summarizes the prior art in the area of current sensorless control ofsingle phase boost-type SMR.

SUMMARY

In the disclosed examples, power supply control can be provided withoutcurrent sensors in the form of resistors or Hall Effect current sensors.Steady state and transient performance can be achieve that is comparableto schemes with sensed current by estimating the current from theinductor voltage and minimizing (or reducing) the current THD by arobust inductor parameter estimation technique.

In typical examples, digital power supply controllers comprise a logicdevice, having computer executable instructions defined therein forperforming a control method that includes receiving a measurementcorresponding to a switch voltage associated with a switch device and ameasurement of a rectified input voltage. Based on the switch voltageand the rectified input voltage, a resistance and an inductance of aboost inductor are estimated. A current in the inductance is estimatedbased on the estimated resistance and inductance, and a power controlsignal is obtained based on the estimated current.

The foregoing and other features, and advantages of the invention willbecome more apparent from the following detailed description, whichproceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a single-phase SMR.

FIGS. 2A-2B illustrate an inductor model and estimation of inductorcurrent, respectively.

FIG. 3 illustrates an ideal inductor current i_(L) and inductor voltagev_(L).

FIG. 4 illustrates input voltage and current under full-load (top) andhalf-load (bottom). The voltage waveform has been scaled to 1/50 of itsoriginal value.

FIGS. 5A-5B illustrate input current (i_(in)), the output voltage(v_(o)) and the output of the voltage controller (κ) when the load waschanged from 100% to 50% and 50% to 100%, respectively.

FIG. 6 illustrates RMS value of input voltage (V_(in)), input current(i_(in)), the output voltage (v_(o)) and the output of the voltagecontroller (κ) when the RMS value of input voltage (V_(in)) was changedfrom 132 V to 108 V and again from 108 V to 132 V.

FIGS. 7A-7B illustrate inductor model based current estimation alongwith parameter adaptation, and low pass filtering of estimatedinductance for inductor model, respectively.

FIGS. 8A-8C illustrate (8A) parameter adaptation time for L⁰=16 mH andvarious values of R_(L) ⁰ (left) and for R_(L) ⁰=1.2Ω and various valuesof L⁰ (right), and (8B) parameter convergence trajectory for variousinitial values L⁰ and R_(L) ⁰ in 2-D (left) and 3-D (right) with time,and (8C) steady state simulated input current for different values ofL^(imp) and R_(L) ^(imp).

FIG. 9 illustrates hardware setup.

FIGS. 10A-10B illustrate B-H curve for type 40 material and type 2Dmaterial, respectively.

FIGS. 11A-11B illustrate actual input current i_(in) at full-load andhalf-load and input voltage v_(in) when measured current was used forcurrent feedback, actual input current when computed current was usedfor current feedback. Type 40 core material was used for the inductor,respectively. L^(imp)=11 mH, R_(L) ^(imp)=0.6Ω.

FIGS. 12A-12B illustrate measured (grey) and computed (black) inductorcurrent when the computed current is used for the current control withimproved (type 2D material) inductor design at rated load, and actualinput current i_(in) at full-load and input voltage v_(in) when thecomputed current was used for current feedback with the improvedinductor, respectively. L^(imp)=6.5 mH, R_(L) ^(imp)=1.0Ω.

FIGS. 13A-13B illustrate step change from full load to half load withmeasured current feedback, and computed current feedback using theimproved inductor, respectively.

FIGS. 14A-14B illustrate step change from half load to full load withmeasured current feedback, and computed current feedback using theimproved inductor, respectively.

FIGS. 15A-15B illustrate L^(est) (top) and R_(L) ^(est) (bottom) for 200line half-cycles without model adaptation but controlled with computedcurrent at rated load (201 W), and input current, before (top row) andafter (bottom row) model adaptation at rated load, with L⁰=16 mH, R_(L)⁰=0.9Ω, (left); with L⁰=6 mH, R_(L) ⁰=1.2Ω, (right), respectively.

FIGS. 16A-16B illustrate an inductor model parameter adaptation forL⁰=16 mH and various values of R_(L) ⁰, (6A); and R_(L) ⁰=1.5Ω variousvalues of L⁰, (6B).

FIG. 17A illustrates a boost convertor circuit.

FIGS. 17B-17C illustrate amplifier/buffer circuits for voltagemeasurement and switch transistor control.

FIG. 18 illustrates a representative method of estimating inductorresistance and inductance.

DETAILED DESCRIPTION

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” does not exclude the presence ofintermediate elements between the coupled items.

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or perfoimed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus’ are referred to as“lowest”, “best”, “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.

The disclosed methods and apparatus can be implemented in a variety ofhardware devices, referred to herein as logic devices. Typical examplesin programmable logic devices (PLDs) such as complex PLDs that canimplemented as series of interconnected PLDs. In some examples, thedisclosed methods are transferred to the devices after incorporationwith other power supply or power control hardware. Other examplesinclude field-programmable gate arrays (FPGAs). In some cases,computer-executable instructions for implementing the disclosed methodsare stored in a PROM, EEPROM, or other ROM, or other volatile ornon-volatile memory for transfer to a PLD or FPGA. In other examples,ASICs or other devices (including computer CPUs, systems on a chip(SOC), or other hardware is used. These devices are referred to forconvenience as logic devices, and the disclosed approaches permitdigital power control based on executable instructions implement usingone or more logic devices.

In some examples, voltages are directly measured but such measuredvoltages also refer to voltages derived from resistive or other dividernetworks.

In the disclosed examples, methods and apparatus that implement novel,non-obvious approaches to estimating inductor current in switching powersupplies are described. As discussed above, inductor current can beindirectly measured by connecting a capacitor in series with a resistoracross a boost inductor. If v_(C) _(s) (s) and i_(L)(s) are respectivelythe capacitor voltage and inductor current in frequency domain, it canbe shown that

$\begin{matrix}{\frac{v_{C_{s}}(s)}{i_{L}(s)} = {\frac{R_{L} + {sL}}{1 + {{sR}_{C_{s}}C_{s}}} = {{R_{L}\frac{1 + {s\frac{L}{R_{L}}}}{1 + {{sR}_{C_{s}}C}}} = {R_{L}\frac{1 + {s\; \tau_{L}}}{1 + {s\; \tau_{C}}}}}}} & (7)\end{matrix}$

wherein R_(L), R_(C) _(s) are respectively the equivalent seriesresistance of the boost inductor L and the external resistor connectedin series with the current sense capacitor C_(s). If τ_(C)=R_(C) _(s)C_(s) is chosen so that it matches

${\tau_{L} = \frac{L}{R_{L}}},$

the relation

$\frac{v_{C_{s}}}{i_{L}}$

becomes frequency independent, signifying that the sensing preserves theshape of the inductor current. Under this condition, v_(C) _(s) isproportional to the inductor current and therefore can be used in thecurrent control loop. This technique is load dependent as both theinductor resistance and the inductor value are influenced by theinductor current. A similar approach can be applied to a dc-dc buckconverter using a self-tuning digital filter whose parameters are tunedusing a test current sink, consisting of a known resistor in series witha small switch, in parallel with the load.

However, as disclosed herein, parameters of a low pass filter used toestimate the inductor current can be determined without using any extracomponents, but can be tuned continuously using a readily implementableapproach. Referring to FIG. 1A, an inductor 102 (referred to in somecases as a “boost” inductor and shown in FIG. 1A as a seriesresistance/inductance combination) is coupled to a rectifier 104, shownas a full wave bridge. The rectifier 104 receives an inputvoltage/current and produces an input rectified voltage v_(d). As shownin FIG. 1, a voltage across the inductor L is obtained first bysubtracting the switch voltage v_(Q) from the input rectified voltagev_(d). The switch voltage is controlled based on the control device 106,shown as a FET in FIG. 1. This inductor voltage is then passed throughan adaptive low pass filter, employing the inductor's tuned resistanceand inductance values as parameters to obtain the inductor current.These parameters can be continuously or periodically estimated andadapted through a scheme so as to make the current control robustagainst parameter variation. When these updated values are used tocompute the inductor current it shows significant improvement in THD.The performance of the current sensorless scheme is comparable to themeasured current scheme both under steady state and transientconditions. These results are confirmed through simulation andexperimentation.

This new approach can be used to eliminate or reduce problems associatedwith conventional methods to sense current. Current sensing with aresistor is associated with problems such as isolation, noise immunityand power loss, especially in high power converters. Current sensingwith a Hall Effect sensor is typically associated with high cost and dcoffset. Conventional current sensorless schemes suffer from the lack ofparameter estimation. With the disclosed approaches, parameters can beestimated and estimation errors can be compensated through closed loopcontrol.

One commercially important example pertains to boost-type SMRs as theyare widely used as front end to dc to dc, ac-dc converters, motorsdrives.

A. Estimation of Inductor Current

Since the measured inductor current as feedback signal for the currentcontrol loop is not available, it was estimated in the following way.First the inductor's inductance and its equivalent series resistance aremodeled as shown in FIG. 2A, The estimated current i_(L) ^(est) can beobtained by solving (8) in real time as shown in FIG. 2B. The inductorvoltage v_(L) ^(mes) is obtained by subtracting v_(Q) ^(mes) from v_(d)^(mes), the measured values of v_(d) from v_(Q), as shown in (9). v_(d)^(mes) and v_(Q) ^(mes) can be acquired by inexpensive resistivenetworks. To avoid integration offset, the integrator is reset at everyzero crossing of the input AC voltage v_(in).

$\begin{matrix}{v_{L}^{mes} = {{R_{L}^{est} \cdot i_{L}^{est}} + {L^{est}\frac{i_{L}^{est}}{t}}}} & (8) \\{v_{L}^{mes} = {v_{d}^{mes} - v_{Q}^{mes}}} & (9)\end{matrix}$

B. Estimation of Inductor Parameters

Assuming ideal inductor current, voltage and parameters, (8) can berewritten in the generic form following FIG. 3 as

$\begin{matrix}{{{v_{L} = {{R_{L}i_{L}} + {L\frac{i_{L}}{t}}}};{0 \leq {\omega \; t} \leq \pi}}{wherein}} & (10) \\{i_{L} = {{\hat{I}}_{L}\sin \; \omega \; t}} & (11)\end{matrix}$

and where ω is the frequency of v_(in) rad./s. and Î_(L) is the peak ofthe inductor current. Differentiating (11) yields

$\begin{matrix}{\frac{i_{L}}{t} = {{\hat{I}}_{L}\omega \; \cos \; \omega \; t}} & (12)\end{matrix}$

Integrating (10) by substituting (11) and (12) in (10) over two instantst₁, t₂, yields

$\begin{matrix}{{{{\int_{t_{1}}^{t_{2}}{v_{L}\ {t}}} = {{R_{L}{\hat{I}}_{L}\frac{1}{\omega}\left( {{\cos \; \omega \; t_{1}} - {\cos \; \omega \; t_{2}}} \right)} + {L{{\hat{I}}_{L}\left( {{\sin \; \omega \; t_{2}} - {\sin \; \omega \; t_{1}}} \right)}}}};t_{1}},{t_{2} \in \left\lbrack {0,\frac{\pi}{\omega}} \right\rbrack}} & (13)\end{matrix}$

Then with

$t_{1} = {{0\mspace{14mu} {and}\mspace{14mu} t_{2}} = {\frac{T}{2} = \frac{\pi}{\omega}}}$

$\begin{matrix}{{\int_{t_{1}}^{t_{2}}{v_{L}\ {t}}} = {{\int_{0}^{\frac{T}{2}}{v_{L}\ {t}}} = {2R_{L}{\hat{I}}_{L}\frac{1}{\omega}}}} & (14)\end{matrix}$

and with

${t_{1} = 0},{t_{2} = {\frac{T}{4} = \frac{\pi}{2\; \omega}}}$

$\begin{matrix}{{\int_{t_{1}}^{t_{2}}{v_{L}\ {t}}} = {{\int_{0}^{\frac{T}{4}}{v_{L}\ {t}}} = {{R_{L}{\hat{I}}_{L}\frac{1}{\omega}} + {L{\hat{I}}_{L}}}}} & (15)\end{matrix}$

Since v_(L) and hence ∫_(t) ₁ ^(t) ² v_(L) dt can be measured, L andR_(L) can be found out using (14) and (15) provided Î_(L) is known. Anestimate of Î_(L) can be obtained from the output voltage ripple [27] asfollows. Since

$\begin{matrix}{{{v_{0,{rip}} \approx {\frac{1}{C}{\int{i_{C}{t}}}}} = {{- \frac{I_{0}}{2\omega \; C}}\sin \; 2\omega \; t}}{and}} & (16) \\{I_{0} = \frac{{\hat{V}}_{d}{\hat{I}}_{L}}{2V_{0}}} & (17)\end{matrix}$

an estimate of Î_(L) can be made from (16) and (17). Here {circumflexover (V)}_(d) is the peak of v_(d), and V₀ and I₀ are the mean values ofoutput de voltage and load current, respectively. If {circumflex over(V)}_(0,rip) is the peak of the output voltage ripple, then using (16)an estimate of Î_(L) can be found, using the nominal value C^(nom) of C,as

$\begin{matrix}{{\hat{I}}_{L}^{est} = {4\omega \; {C^{nom} \cdot \frac{V_{o}^{mes}}{{\hat{V}}_{d}^{mes}} \cdot {\hat{V}}_{o,{rip}}^{mes}}}} & (18)\end{matrix}$

Thus finally the estimates R_(L) ^(est) and L^(est) for R_(L) and L areevaluated using (14), (15) and (18) as

$\begin{matrix}{R_{L}^{est} = {\frac{\omega}{2{\hat{I}}_{L}^{est}}{\int_{0}^{T/2}{v_{L}^{mes}\ {t}}}}} & (19) \\{L^{est} = {\frac{1}{{\hat{I}}_{L}^{est}}\left\lbrack {{\int_{0}^{T/4}{v_{L}^{mes}\ {t}}} - {\frac{1}{2}{\int_{0}^{T/2}{v_{L}^{mes}\ {t}}}}} \right\rbrack}} & (20)\end{matrix}$

It is to be noted that although (18) and hence (19) and (20) aredependent on the actual value of C, it is corrected by the feedbackmechanism of the voltage control loop in the following way. Equation (8)can be written in the Laplace domain as

$\begin{matrix}{{i_{L}^{est}(s)} = {\frac{1}{L^{est}}\frac{1}{\left( {s + \frac{R_{L}^{est}}{L^{est}}} \right)}{v_{L}^{mes}(s)}}} & (21)\end{matrix}$

Since the term Î_(L) ^(est) cancels out in the computation of

$\frac{R_{L}^{est}}{L^{est}},$

only the gain

$\frac{1}{L^{est}}$

is affected by Î_(L) ^(est) in (21). However the voltage control loopcompensator structure is such that it will suitably adjust its gain inorder to make i_(L) ^(est)(s) equal to i_(L) ^(ref) (s) which is theproduct of the rectifier output voltage v_(d) and the output of thevoltage controller κ. The concept is further explained and validated inthe next section. It will be apparent that other time intervals can beselected for performing the above estimates, but intervals of [0, π/4ω]and [0, π/2ω] are convenient.

C. Simulation Results

A 200 W, 120 Vrms, 60 Hz input, 380V DC output, 20 kHz switchingfrequency converter, the details of which are given in the Appendix, wasfirst simulated using the proposed technique to prove the concept.MATLAB/SIMULINK based SimPowerSystems toolbox was used for thesimulation. Standard state-space averaging technique was used following[27] to model the plant transfer functions of the converter for both thecurrent loop and the voltage loop. Both the current controller and thevoltage controller is Type II [28] and are of the form as shown in (22).

$\begin{matrix}{{G_{c}(s)} = {K\frac{s + \omega_{z}}{s\left( {s + \omega_{p}} \right)}}} & (22)\end{matrix}$

The open loop crossover frequency of the current loop and the voltageloop were chosen to be 3183 Hz (that is

$\frac{1}{2\pi}$

or switching frequency) and 10 Hz (for a good compromise between currentharmonic content and transient response) respectively, based on standarddesign practice. Because of the pole at zero frequency in thecontroller, the steady state dc error is zero. This is the reason whythe estimation of

$\frac{1}{L^{est}}$

is corrected by the voltage feedback controller despite inaccuracies incomputation of Î_(L) ^(est) and hence L^(est) due to capacitortolerance. This is verified later in this section using simulationresults.

FIG. 4 shows the input voltage and input current of the simulatedconverter under half load and full load condition with L=8 mH andR_(L)=0.6Ω (these parameters values were used for both the inductor andcontroller) with sensorless current control. Table II shows theindividual current harmonics and the THD (for 1 s current data andincluding harmonics up to nearly 500 kHz). It is very clear that thescheme produces high quality input current although no capacitor wasincluded at the output of the rectifier in simulation.

FIG. 5 shows the input current (i_(in)), the output voltage (v_(o)) andthe output of the voltage controller (κ) when the load was changed from100% to 50% and 50% to 100% respectively. FIG. 6 shows the inputcurrent, the output voltage and the output of the voltage controllerwhen the RMS value of the input voltage (v_(in)), which is nominally 120V RMS, is changed from 132 V RMS to 108 V RMS and then back again to 132V RMS. The same parameter values as used under the steady statecondition were used for both the boost inductor and the controller.Although no feedforward control schemes were used the performance of theconverter even under transient conditions with sensorless currentcontrol is quite satisfactory.

TABLE II Simulation results. RMS values of the low-order harmonics ofthe input current in mA and its total harmonic distortion for differentoutput powers (100%, 75%, 50% and 25% of rated load). P_(o) I_(in(1))I_(in(3)) I_(in(5)) I_(in(7)) I_(in(9)) I_(in(11)) THD 200 W 1699 27.510.7 9.8 8.8 7.9 2.3% 150 W 1274 23.1 10.5 9.4 8.2 7.2 2.7% 100 W 85219.1 10.6 9.1 7.7 6.2 3.5%  50 W 431 17.1 11.4 8.7 6.2 4.2 6.4%

FIG. 7A illustrates a convertor with a digital control system 702. Oncethe parameters R_(L) ^(est) and L^(est) have been estimated using(18)-(20) in a parameter estimation block 704 they are first passedthrough a low pass filter 706 to smooth out the estimates that areupdated every line half cycle. The low pass filter 706 will also preventany disturbance this update procedure may cause to the voltage controlloop. Suitable time constants for the filters were found to be 40 msthrough simulation for the adaptation of both L and R_(L). At the startof the simulation, the inductor model uses pre-assigned values of L⁰,R_(L) ⁰ as the initial values of the low-pass filter. Once the converterreaches steady state, the parameter adaptation is activated after 0.5 s.The inductor model then uses L^(imp), R_(L) ^(imp) as the parameters.The SIMULINK model used to implement the scheme for the inductance isshown in FIG. 7B. Until 0.5 s, the relay block selects L⁰ which getssubtracted from itself. The input to low pass filter block is thus zero.Therefore the output from the low pass filter, which is also zero, whenadded to L⁰ makes L^(imp)=L⁰ (given as ‘L_0’ and ‘L_imp’ in FIG. 7B.After 0.5 s, L^(est) (given as ‘L_comp’ in FIG. 7 b) is selected by therelay causing L^(imp) to reach L^(est) after the time delay imposed bythe low pass filter. An identical block computes R_(L) ^(imp). Theequations for L^(imp) and R_(L) ^(imp) are shown in (23) and (24)respectively.

$\begin{matrix}{L^{imp} = \left\{ \begin{matrix}L^{0} & {{{for}\mspace{14mu} t} \leq {0.5s}} \\{{L^{0}^{{- 0.04}{({t - 0.5})}}} + {L^{est}\left\{ {1 - ^{{- 0.04}{({t - 0.5})}}} \right\}}} & {{{for}\mspace{14mu} t} > {0.5s}}\end{matrix} \right.} & (23) \\{R_{L}^{imp} = \left\{ \begin{matrix}R_{L}^{0} & {{{for}\mspace{14mu} t} \leq {0.5s}} \\{{R_{L}^{0}^{{- 0.04}{({t - 0.5})}}} + {R_{L}^{est}\left\{ {1 - ^{{- 0.04}{({t - 0.5})}}} \right\}}} & {{{for}\mspace{14mu} t} > {0.5s}}\end{matrix} \right.} & (24)\end{matrix}$

The stability and the time required for convergence of the adaptedparameters were investigated next. FIG. 8A shows the adaptationconvergence time for various values of R_(L) ⁰ for a fixed value of L⁰and also for various values of L⁰ for a fixed value of R_(L) ⁰. It isseen that higher these initial values are, the shorter is the time foradaptation. Also the final adapted values of the parameters convergedvery closely to the true value of the inductor. For example, for theresults shown in FIG. 8A these parameters converged to 8.025 mH and0.59Ω after 1.5 s of simulation when the true values were 8 mH and 0.6Ω.FIG. 8B describes the convergence trajectories both in 2-D and 3-D (withtime) for the various R_(L) ⁰ and L⁰ values. The gray circles in themiddle of these plots depict the true parameters.

The need for parameter estimation and adaptation can be understood fromthe plot matrix presented in FIG. 8C. Without parameter estimation andadaptation, as the time constant τ^(imp)=L^(imp)/R_(L) ^(imp) increasedfrom the true value 8 mH/0.6Ω=13.33 ms, the input current waveforms inthe lower triangular elements become more peaked in nature. However themore τ^(imp) decreased below its true value of 13.33 ms, the more itlooks like a square wave, as can be seen from the upper triangularelements of the plot matrix. Thus from the point of peak current ratingof the power devices it is best to start with the lowest possibleinitial value of L^(imp) and the highest possible initial value of theresistance R_(L) ^(imp). This however will increase the parameterconvergence time as discussed earlier. It is also noted from thediagonal elements of FIG. 8( c) that regardless of the initial value ofL^(imp) and R_(L) ^(imp), the steady state current waveforms areidentical as long as the time constant τ^(imp) matches the true value;meaning that the control loop corrects for any error in the estimationof L as pointed out earlier. This was also verified by noting thedifferent values of κ in Table III for incorrect values L^(imp) andR_(L) ^(imp) but the correct value τ^(imp). As L^(imp) changes, κchanges too, such that the product κ·L^(imp) is maintained constant.

TABLE III Different values of voltage controller output for the correctvalue of τ^(imp) = 13.33 ms but incorrect values of L^(imp) and R_(L)^(imp). The voltage controller output κ changes such that the product κ· L^(imp) remains constant in order to keep i_(L) ^(est) ≡ i_(L) ^(ref).  L^(imp) [mH]     R_(L) ^(imp) [Ω]$\frac{L^{imp}}{R_{L}^{imp}}\mspace{14mu}\lbrack{ms}\rbrack$  $\kappa \mspace{14mu}\left\lbrack \frac{A}{V} \right\rbrack$     κ ·L^(imp) [s]  4 0.3  13.33 0.028  112 · 10⁻⁶  6 0.45 13.33 0.019  112 ·10⁻⁶  8 0.6  13.33 0.014  112 · 10⁻⁶ 12 0.9  13.33 0.0092 111 · 10⁻⁶ 161.2  13.33 0.0069 110 · 10⁻⁶

D. Experimental Results

A single-phase boost topology based SMR circuit, similar to the onesimulated, was built in the laboratory. A digital signal controller(DSC) TMS320F2812 from Texas Instruments [30] embedded on an evaluationboard eZdsp F2812 from Spectrum Digital [31, 32] was used forcontrolling and parameter adaptation of the boost inductor. FIG. 9 showsthe hardware setup. The TMS320F2812 controller is meant primarily formotor drives application and has a low clock speed. It also uses fixedpoint arithmetic. Further, to improve accuracy and precision of theestimated current and hence the THD of the input current, v_(d), v_(Q)and v_(o) were sampled 40 times within one switching cycles. Thesefactors limited the switching frequency of the converter to 20 kHz assignificant real time computations are also involved for determining theduty cycle. For higher switching frequency either a floating pointcontroller or one with higher clock speed should be used. Alternatively,the method used in [26] can be followed whereby the average inductorvoltage v_(L,av)[k] for every k^(th) switching cycle is computed as in(25) using the corresponding values of input and output voltagesv_(d)[k] and v₀[k] respectively and the duty cycle d[k]. v_(L,av)[k] isthen used to compute the inductor current. This will eliminate the needof sampling v_(Q) and large number of samples within one switchingcycle.

v _(L,av) [k]=v _(d) [k]−(1−d[k])v ₀ [k]  (25)

However, [26] reported an accuracy of 6% or better using a maximumsampling rate of 8 times switching frequency. With the procedurefollowed for the work presented here, the maximum inaccuracy inestimating the transition point of v_(Q) is only

${\left( \frac{1}{40} \right)*100\%} = {2.5{\%.}}$

To avoid errors due to analog-to-digital conversion in measuring thepeak of the output voltage ripple {circumflex over (V)}_(o,rip) ^(mes),to estimate Î_(L) ^(est), the peak of inductor current, the followingtechnique was used. Neglecting higher order harmonics in the outputripple except the second, the output can be approximated as

v _(o) ≈V _(o) −{circumflex over (V)} _(o,rip) sin 2ωt  (26)

Then,

$\begin{matrix}{{{\hat{V}}_{o,{rip}} = {\frac{\omega}{2}\left\lbrack {{\int_{T/4}^{T/2}{\left( {v_{o} - V_{o}} \right)\ {t}}} - {\int_{0}^{T/4}{\left( {v_{o} - V_{o}} \right)\ {t}}}} \right\rbrack}},{T = \frac{2\pi}{\omega}}} & (27)\end{matrix}$

where V_(o) is the average value of the output voltage. Equation (27)can be used with V₀*, the output voltage reference instead of V₀. Thisway, it is not necessary to find V₀. If, because of a small regulationerror, the actual output voltage differs slightly from its reference,both integrals in (27) are equally affected and the subtractioneliminates the impact on the result.

The controllers given by (22) were implemented in the digital domainusing bilinear transformation [33].

The converter initially used a boost inductor made with type 40 powderediron core material [34]. The type 40 material has considerablenonlinearity and hysteresis as shown by the B-H curve in FIG. 10A. Atfirst the inductor parameters were estimated through trial and error bycomparing the measured current with the computed current as the nominalvalues of inductor parameters did not produce satisfactory results.However when computed current feedback was used instead of measuredcurrent feedback as shown in FIG. 11, the actual current waveform wasdistorted. For example, the regions θ₁ and θ₂ in the second quartercycle of the current waveform deviated considerably from the expectedsinusoidal nature. Such behaviour can occur if the inductor isnonlinear, that is, if the core has a nonlinear relationship betweenmagnetic field strength, H and magnetic flux density, B. Allferromagnetic materials exhibit some degree of saturation andhysteresis. To circumvent this problem, an inductor made out of type 2Dpowdered iron core material [34], whose B-H curve shows (FIG. 10B) morelinearity and less hysteresis, was tried. However, the relativepermeability of the type 2D core is lower and hence it required a largercore and more number of turns to build the inductor. This increased theoverall cost and size of the inductor. It should however be possible tooptimize the inductor design using other core materials such as gappedferrites, but it was not pursued at this point of time as the objectiveof this work is different. FIGS. 12A-12B show the improvement in theestimated current with the changed inductor. Incidentally, in order toimprove the THD, a sine wave generated by the controller andsynchronized with the utility voltage was used as current reference.

Subsequently, the transient behaviour of the scheme was tested using theimproved inductor. FIG. 13A-13B compare the performance of thesensorless current feedback with a resistor-based measured currentfeedback when load was changed from full load to half load. FIGS.14A-14B compare the performance of the two schemes when load was changedfrom half load to full load. Except for very slight increase intransient response time with the sensorless current feedback, the twoschemes seem quite comparable. It is to be noted that parameteradaptation was disabled when these tests were performed to avoid itsinterference with the load transient.

Before the inductor model was made adaptive, i.e. L^(est) and R_(L)^(est) are used in determining L^(imp) and R_(L) ^(imp) respectively,the estimated model parameters were inspected. To do this, the valuesfrom 200 line half-cycles were stored in the controller and thenretrieved from the memory. These values are plotted in FIG. 15A forrated load when the computed inductor current was used for the currentcontrol. As can be seen the results are quite consistent and fall withina narrow band. Also both L^(est) and R_(L) ^(est) follow similar trend.Hence they were deemed acceptable for parameter adaptation. Also thelow-pass filters described in FIG. 4 b help in filtering out much of thescattering and provide an averaged update. Table IV provides the resultsfor the average value and standard deviation of L^(est) and R_(L) ^(est)under different load conditions for values obtained from 200 line halfcycles.

TABLE IV Average values and standard deviations of L^(est) and R_(L)^(est) under different load conditions for values obtained from 200 linehalf cycles.     P_(o)     L_(av) ^(est) [mH]$\frac{\sigma_{L}}{L_{av}^{est}}$     R_(L,av) ^(est) [Ω]$\frac{\sigma_{R_{L}}}{R_{L,{av}}^{est}}$ 201 W 6.40  9.0% 1.32 10.9%151 W 6.01 14.9% 1.37 15.9% 101 W 5.68 12.8% 1.48 13.2%  51 W 4.90 19.3%1.21 15.5%

FIG. 15B shows the effect of the model adaptation on the input currentfor two cases of initial parameters. It shows the input currentwaveforms before and after the inductor model is adapted. Comparing themwith FIG. 8C readily reveals that with L⁰=16 mH and R_(L) ⁰=0.9Ω,

$\tau^{0} = \frac{L^{0}}{R_{L}^{0}}$

is above the actual value whereas with L⁰=6 mH, R_(L) ⁰=1.2Ω it is belowthe actual one.

FIGS. 16A-16B show L^(imp) and R_(L) ^(imp) with respect to time fordifferent initial values. After the adaptation is turned on at t=0, theimplemented parameters asymptotically approach the estimated values.These results are close to the ones obtained through simulation andplotted in FIG. 8A. However the dependence of convergence time on theinitial L⁰ seems much less. One reason could be the inductor'stemperature rise which increased R_(L). When L⁰ was set to values lessthan 6 mH, the current control became unstable and large oscillationsoccurred in the input current. In all other tested cases, the modeladaptation converges to around 6.1 mH and between 1.3 and 1.5Ω. Apossible workaround to avoid the instability is to use a value of L⁰larger than the nominal value such that this situation is avoided. Thecontrol is more robust and the THD is less when L⁰ has a larger value.

Table V lists the comparative THD results between simulated andexperimental results with measured current feedback and estimatedcurrent feedback with and without parameter estimation with two sets ofL⁰ and R_(L) ⁰. Table VI lists THD values at other loads only withparameter adaptation. The results clearly show that parameter adaptationis very important for improvement of THD and hence power factor.

Finally, the efficiency was also tested at various load levels with thescheme as shown in Table VII. The calculation did not include the powerfed to the auxiliary power supply (in the order of mW) and the power forthe digital controller board.

TABLE V Comparison of low-order harmonics of the input current as % ofthe fundamental and its THD for simulation, control with measuredcurrent and control with estimated current before and after modeladaptation at rated load. harmonic 2 3 5 7 9 11 THD simulated 0 1.6 0.60.6 0.5 0.5 2% control with measured current 0 2.0 1.8 0.4 0.6 1.4 3%control with before 1 13.3 9.3 4.5 1.5 2.4 17%  estimated currentadaptation L⁰ = 16 mH after 4 2.0 2.8 1.7 0.6 1.2 4% R_(L) ⁰ = 0.9 Ωadaptation control with before 3 12.2 8.5 4.4 1.7 2.1 15%  estimatedcurrent adaptation L⁰ = 6 mH after 0 3.8 3.1 2.3 1.1 0.9 6% R_(L) ⁰ =1.2 Ω adaptation

TABLE VI Low-order harmonics of the input current as % of thefundamental and its THD after model adaptation at various load levels.harmonic 2 3 5 7 9 11 THD L⁰ = 16 mH P_(o) = 150 W 1 2.1 2.5 1.5 0.6 1.04% R_(L) ⁰ = 0.9 Ω P_(o) = 100 W 3 3.2 2.2 2.3 0.9 2.2 6% P_(o) = 50 W 313.5 7.6 4.6 1.5 3.1 17%  L⁰ = 6 mH P_(o) = 150 W 4 3.9 1.8 1.6 1.0 1.25% R_(L) ⁰ = 1.2 Ω P_(o) = 100 W 9 5.7 2.8 1.7 1.3 1.5 7%

TABLE VII Converter efficiency at various loads P_(o) 198 W 150 W 100 W50 W η 0.94 0.92 0.91 0.86

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

We claim:
 1. A digital power supply controller, comprising: a logicdevice, having computer executable instructions defined therein forperforming a method comprising: receiving a measurement corresponding toa switch voltage associated with a switch device and a measurement of arectified input voltage, and based on the switch voltage and therectified input voltage, estimating a resistance and inductance of aboost inductor; estimating a current in the inductance based on theestimated resistance and inductance; and determining a control signalfor the switch device based on the estimated current.
 2. The digitalpower supply controller of claim 1, further comprising estimating aboost inductor voltage based on the measurement corresponding to theswitch voltage associated with a switch device and the measurement ofthe rectified input voltage.
 3. The digital power supply controller ofclaim 1, further comprising: estimating a magnitude of a periodic boostinductor current based on an output voltage ripple; and estimating theresistance and the inductance of the boost inductor based on theestimated magnitude.
 4. The digital power supply controller of claim 3,further comprising estimating the boost inductor based on a differencebetween the measurement corresponding to the switch voltage associatedwith the switch device and the measurement of the rectified inputvoltage.
 5. The digital power supply controller of claim 4, wherein theresistance and inductance of the boost inductor are estimated based onintegration of the relation$v_{L}^{est} = {{R_{L}^{est}i_{L}^{est}} + {L^{est}\frac{i_{L}^{est}}{t}}}$over at least two different time intervals, wherein v_(L) ^(est), R_(L)^(est), i_(L) ^(est), L^(est) are the estimated boost inductor voltage,the estimated boost inductor resistance, the estimated boost inductorcurrent, and the estimated boost inductor inductance, respectively. 6.The digital power supply controller of claim 5, wherein the estimatedboost current is periodic at an angular frequency ω.
 7. The digitalpower supply controller of claim 6, wherein the estimated boost inductorcurrent is expressed as i_(L) ^(est)=I_(L) ^(est) sin(ωt+φ), whereinI_(L) ^(est) is the estimated magnitude of the periodic boost inductorcurrent and φ is an arbitrary phase.
 8. The digital power supplycontroller of claim 7, wherein the at least two different time intervalsinclude at least one of the intervals (0, π/ω) and (0, π/2ω).
 9. Thedigital power supply controller of claim 7, wherein the at least twodifferent time intervals differ by about ¼ of a period of the estimatedboost inductor current.
 10. The digital power supply controller of claim1, wherein the control signal for the switch device is determined basedon the estimated current and a reference voltage or current.
 11. Thedigital controller of claim 1, wherein the method further comprisesapplying a low pass filter defined by the estimated boost inductorresistance and inductance so as to estimate the inductor current fromthe inductor voltage.
 12. A boost power supply, comprising: the digitalpower supply controller of claim 1; an input rectifier; a boost inductorcoupled to the input rectifier; and a switch coupled to the boostinductor and the digital power supply controller that operates theswitch so as to select an output voltage.
 13. A boost-mode switchingpower supply, comprising: at least one rectifier that receives an inputvoltage and produces a rectified output voltage; a switching element; aboost inductor situated to electrically connect the rectified outputvoltage to the switching element at a first switching element terminal’;a diode in series with the inductor and coupled to an output; a digitalcontroller coupled to a control input of the switching element, thedigital controller situated to receive measured values of the rectifiedinput voltage and a switch voltage, produce an estimate of an inductorresistance current and based on the received measured values, and couplea control signal to control input of the switching element based on theestimated inductor resistance and inductance.
 14. The boost mode powersupply of claim 13, wherein the digital controller includes a digitallow pass filter.
 15. The boost mode power supply of claim 14, whereinthe digital controller is coupled to a reference voltage, and thecontrol signal is based on the reference voltage.
 16. A method,comprising: estimating a boost inductor resistance and inductance basedon measured voltages associated with a rectified input voltage and aswitch voltage; and based on the estimated inductor resistance andinductance, defining a control signal for a switching transistor; andcoupling the control signal to the switching transistor.
 17. The methodof claim 16, wherein the switching transistor is a FET.
 18. The methodof claim 16, wherein the resistance and inductance of the boost inductorare estimated based on integration of the relation$v_{L}^{est} = {{R_{L}^{est}i_{L}^{est}} + {L^{est}\frac{i_{L}^{est}}{t}}}$over at least two different time intervals, wherein v_(L) ^(est), R_(L)^(est), i_(L) ^(est), L^(est) are the estimated boost inductor voltage,the estimated boost inductor resistance, the estimated boost inductorcurrent, and the estimated boost inductor inductance, respectively. 19.The method of claim 18, wherein the estimated boost inductor current isexpressed as i_(L) ^(est)=I_(L) ^(est) sin(ωt+φ), wherein I_(L) ^(est)is the estimated magnitude of the periodic boost inductor current and ωis an angular frequency and φ is an arbitrary phase.
 20. The method ofclaim 19, wherein the at least two different time intervals include atleast one of the intervals (0, π/ω) and (0, π/2ω) or intervals thatdiffer by ¼ period of the rectified input voltage.